Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
  Case Tag  
Price  
Sales  
Tax %  
Raw Total  
Incl. Sales Tax  
Rounded  
to Penny  
Rounded  
to Nickel  
Rounded  
to Dime  
  Purchase #1 $73.49   12.449%   $82.6388   $82.64   $82.65   $82.60  
  Purchase #2 $200.92   6.868%   $214.7192   $214.72   $214.70   $214.70  
  Purchase #3 $58.54   4.199%   $60.9981   $61.00   $61.00   $61.00  
  Purchase #4 $77.99   4.745%   $81.6906   $81.69   $81.70   $81.70  
  Purchase #5 $167.71   10.794%   $185.8126   $185.81   $185.80   $185.80  
  Purchase #6 $147.73   3.866%   $153.4412   $153.44   $153.45   $153.40  
  Purchase #7 $64.29   9.779%   $70.5769   $70.58   $70.60   $70.60  
  7 purchase totals = $790.67       $849.8774   $849.88   $849.90   $849.80